In order to enable a plurality of users to simultaneously use limited radio resources, a multiplexing scheme is required. The multiplexing scheme divides a single line or transmission path into a plurality of channels capable of simultaneously transmitting/receiving individual independent signals. There are a variety of multiplexing schemes, for example, a Frequency Division Multiplexing (FDM) scheme for dividing a single line into a plurality of frequency bands and performing signal multiplexing, and a Time Division Multiplexing (TDM) scheme for dividing a single line into a plurality of very short time intervals and performing signal multiplexing.
Currently, due to the increasing demands of multimedia data in mobile communication, a multiplexing method for effectively transmitting a large amount of data is required. A representative multiplexing method is an orthogonal frequency division multiplexing (OFDM) scheme.
The OFDM scheme is indicative of a digital modulation scheme capable of improving a transfer rate per bandwidth and preventing multi-path interference from being generated. The OFDM scheme is characterized in that it acts as a multi-sub-carrier modulation scheme using a plurality of sub-carriers, wherein individual sub-carriers are orthogonal to each other. Therefore, although frequency components of individual sub-carriers overlap with each other, the OFDM scheme is problem free. The OFDM scheme can perform multiplexing of many more sub-carriers than those of a general frequency division multiplexing (FDM) scheme. Thus, high frequency use efficiency is implemented.
A mobile communication system based on the above-mentioned OFDM scheme currently uses a variety of multiple access schemes capable of allocating radio resources to a plurality of users, for example, an OFDM-FDMA (OFDMA) scheme, an OFDM-TDMA scheme, and an OFDM-CDMA scheme, etc. Specifically, the OFDMA (Orthogonal Frequency Division Multiple Access) scheme allocates some parts of all sub-carriers to individual users, such that it can accommodate a plurality of users.
FIG. 1 illustrates a method for allocating radio resources in accordance with the related art. Referring to FIG. 1, a broadband wireless access system comprises a specific configuration of FIG. 1 as a basic unit for allocating OFDMA uplink radio resources. This specific configuration shown in FIG. 1 is referred to as a tile structure. In the case of the above-mentioned tile structure, data of a Channel Quality Indication Channel (CQICH) or data of an Acknowledge Channel (ACKCH) is transmitted via a plurality of data sub-carriers 102, 103, 105, 106, 107, 108, 110, and 111. A pilot channel is transmitted via pilot sub-carriers 101, 104, 109, and 112. Each sub-carrier transmitted via the tile structure is referred to as a constituent unit of the tile structure.